Greenhouse Types

 

Ignoring greenhouse use, there are essentially three basic forms of greenhouse:

                            1. Span
                            2. Lean-to
                            3. ¾-span

 

The Span Greenhouse

This has a double-sloped, or A-shaped, roof and is typically used when no back wall is available. When growing flowers or fruit it is normally positioned with the greenhouse ridge running north and south.

 

Span-roof Greenhouse

The Lean-to Greenhouse

This typically requires a back wall of sufficient height so as to allow a single roofed structure to be built against it. Ideally the lean-to a greenhouse should face south, but is obviously dependent upon the orientation of the back wall.

 

Lean-to Greenhouse

The ¾-Span Greenhouse

This is a hybrid between a span and lean-to. It is generally adopted if the back wall is either not high enough or cannot be made high enough to accommodate a lean-to. It has one long front roof and a shorter back ground which abuts the back wall. Similar to the lean-to, the front roof should ideally face south.

 

3/4 span greenhouse

Which type is best? 

In the firm’s fifth edition Horticultural catalogue, dated around 1925, they offered advice as to the type of roof to adopt:

There is no golden rule governing this point, and a greenhouse in most cases may equally well be roofed as a span, a ¾-span, or a lean-to, available position, existing walls, or preference of customer being in most cases the deciding factor.

Certain trees and plants undoubtedly do better in a certain kind of house: Vines, for instance in a lean-to, Carnations in a span, etc., etc.

One thing it is important to remember: plant houses generally are best kept as low as possible, so that the plants may be near the glass.

The pitch of the roof is important, because if it is too flat it will not carry dry, and the trees or plants are liable to be burnt by the sun.

For a span or ¾-span house a 7-inch or 8-inch pitch is usual. A rise of 7 inches to the foot is a good pitch for narrow lean-to houses, while a 6-inch pitch may be used for wider ones, so as to save height of back wall. A pitch as low as 5 inches rise to the foot can be adopted in special circumstances, though it is not recommended. Expressed in degrees, a 5-inch pitch is an angle of 66 degrees; a 6-inch pitch, of 63 degrees; a 7-inch pitch, of 60 degrees; and an 8-inch pitch, of 57 degrees.